There has been known a focused ion beam system as a system for performing observation, various evaluation or analysis, or the like on a sample such as a semiconductor device, and for preparing a TEM sample by taking a fine and thin sample fragment from a sample and fixing the thin sample fragment to a sample holder.
This focused ion beam system includes an ion source for generating ions, and radiates ions generated in the ion source as a focused ion beam.
There are many types of ion sources. For example, a plasma type ion source and a liquid-metal ion source have been known. Recently, there have been provided a gas field ion source (GFIS) capable of generating focused ion beams having a smaller beam diameter and higher luminance as compared to the above-described ion sources.
The gas field ion source mainly includes an emitter structure having an aciculate emitter with a tip which is sharpened at an atomic level, a gas source for supplying a gas such as helium (He) to the vicinity of the emitter, a cooling unit for cooling the emitter, and an extraction electrode disposed at a position apart from the tip of the emitter.
Here, an emitter structure disclosed in JP-A-2012-098293 will be described briefly.
As shown in FIG. 8, an emitter structure 100 mainly includes a base member 101, a pair of conductive pins 102 fixed to the base member 101, a filament 103 connected between the tips of the conductive pins 102, and the emitter 104 connected to the filament 103.
The emitter 104 is hung and held on the filament 103 in a state where a base end portion of the emitter 104 is connected to the filament 103 by spot welding or the like.
In this configuration, after the gas is supplied to the vicinity of the emitter 104, if an extraction voltage is applied between the emitter 104 and an extraction electrode (not shown) while the emitter 104 is cooled, the gas is ionized into gas ions by a high electric field formed around a tip portion of the emitter 104. Then, the gas ions are drawn toward the extraction electrode repulsively from the emitter 104 having a positive potential. Thereafter, the drawn gas ions are focused while being appropriately accelerated, thereby becoming a focused ion beam.
Especially, since the focused ion beam generated from the gas field ion source has a small beam diameter and narrow energy spread (radiation angle distribution), it is possible to irradiate a sample with the beam having a small beam diameter. Therefore, it becomes possible to improve the resolution during observation or perform finer etching.
Meanwhile, when a crystal structure of the emitter 104 is broken, by supplying electric power from a current source (not shown) to the emitter 104 through the conductive pins 102 and the filament 103 to heat the emitter 104, atoms configuring the emitter 104 are rearranged.
As described above, in the emitter structure 100, since the emitter 104 is held only by the filament 103, transfer of heat to the emitter 104 is performed mainly through the filament 103. In this case, during heating of the emitter 104, or during rearranging of the emitter 104, since the amount of heat radiation from the emitter 104 is small, the emitter 104 is efficiently heated through the filament 103. However, there is a problem in that cooling efficiency is low during cooling of the emitter 104, such as during generating of gas ions.
The ion emission amount of the gas field ion source depends highly on temperature. Thus, it is preferable to operate the gas field ion source at lower temperature.
Also, in the emitter structure 100, since the emitter 104 is held only by the filament 103 as described above, it is difficult to hold the emitter 104 perpendicularly with respect to the base member 101. Since a focused ion beam which is generated from the gas field ion source has a narrow radiation angle distribution as described above, in order to surely radiate the focused ion beam toward a sample, the optical axis of the focused ion beam is required to be aligned with a desired direction.
With respect to this, JP-A-2012-098293 discloses a configuration provided with a gimbal mechanism (tip manipulator) for adjusting the tilt or position of the optical axis of a focused ion beam generated from the emitter 104.
However, the provision of the gimbal mechanism causes problems such as an increase in the number of components, and complication of the system.